1. Field of the Invention
The present invention relates to a sheet feeding device and an image-forming apparatus having same, and more particularly, to an air suctioning-type sheet feeding device which separates sheets from a stack of sheets by blowing air, and feeds the uppermost one sheet that has been separated while air suctioning the sheet, and an image-forming apparatus having the sheet feeding device, such as a printing apparatus including a stencil printing apparatus, a copying apparatus including an electrophotographic copier, a facsimile apparatus, a printer, an inkjet recording apparatus, a plotter or a compound apparatus comprising these plurality of functions.
2. Description of the Related Art
As is widely known, a sheet feeding device (a paper feeding device) for extracting and feeding sheets one at a time from a sheet stack can be a friction type or an air type. In particular, the air-type paper feeding device is for separating sheets from a stack of sheets by blowing/discharging air, and feeding the uppermost one sheet that has been separated while air suctioning the sheet, and for example, the air-type paper feeding devices disclosed in Japanese Patent Laid-open Publication No. 2005-162456 (hereinafter referred to as Prior Art 1), Japanese Patent Laid-open Publication No. 2007-31070 (hereinafter referred to as Prior Art 2), and Japanese Patent Laid-open Publication No. 2007-197097 (hereinafter referred to as Prior Art 3), are known.
In the air-type paper feeding device of the prior art, front air is blown from the front of the paper stack onto the leading edge surface (front edge surface) of the paper stack. Further, side air is also blown onto both side edge surfaces of the paper stack in the same manner. Blowing the respective air onto the leading edge surface and both side edge surfaces of the paper stack like this separates the papers of the upper portion of the paper stack one sheet at a time.
Now then, the prior art side air blowing system includes a system for blowing side air from only one side with respect to the sheet width direction, and a system for blowing side air from both sides with respect to the sheet width direction.
However, these two prior art side air blowing systems suffer from the following problems. That is, first, when using paper (sheets) that are large with respect to the sheet width direction in the side air blowing system that only blows air from the side fence of the one side, for example, in the case of an A3 or A4 width-wise sheet (in other words, a size of 297 mm with respect to the sheet width direction), only one side of the sheet with respect to the sheet width direction lifts and separates; the other side does not lift. If a piece of paper is suctioned onto the suctioning belt in this state, the floating side can be held by suction and conveyed at a low load, but the non-floating side exhibits high conveying resistance, and is conveyed diagonally, that is, results in skewed conveying. In a worst case scenario, the paper is unable to be reliably suctioned and mis-feeding occurs.
Second, in the case of a side blowing system that blows air from both side fences, trouble like that described in the first case above does not occur when using paper that is large with respect to the sheet width direction (A3, and the like), and the lifting, separating and conveying of the paper is stable. However, by contrast, when using paper that is narrow with respect to the sheet width direction, for example, in the case of A5 and narrower paper (a size of 150 mm or less with respect to the sheet width direction), because the air is blown out from side air outlets disposed in the side fences of both sides, the streams of air collide with one another, and the air escapes either toward the front (with respect to the sheet feed direction) or toward the rear. If the air only escapes toward the rear, this is not particularly problematic, but the air also escapes toward the front. The air that escapes toward the front in this case affects the leading-edge part of the loaded paper, causing the paper to move forward on its own. That is, the problem of multi-feed conveying occurs.
As a measure for solving the second problem described above, stopping the side air blowing from the one side when using paper that is narrow with respect to the sheet width direction makes it impossible for the streams of air blowing out from both side fences to collide, and since there are side fences, the air is unable to escape completely.
Further, when this measure is implemented, a side air blowing drive source (DC fan or the like) must be mounted to each side fence, or a stopcock (switching valve) and a drive source (motor or the like) for opening and closing the stopcock is required, thereby driving up costs. It also becomes necessary to exercise control in accordance with the type of paper.